A researcher who works on heat-related illnesses is trying to get high school football coaches to reduce their number of two-a-day preseason football practices. College football adopted this proposal in 2003, but high schools haven't yet. If it's a bad idea to make 20-year-olds do extremely strenuous physical activity twice a day in the sweltering summer heat with lots of padding, it's probably an even worse idea for 15-year-olds.
Even if it turns out that we get lower-quality football out of the reduction in practice time (something that the researcher disputes) it's important to remember that competitive sports aren't too far from being a zero-sum game. If, say, scientists were hampered by restrictions on how much they could study, we'd have lower-quality medicines and plastics and computer chips, and life for everyone wouldn't be as good. But if you hamper both teams in a football game equally, nothing especially valuable is lost. The quality of the play on the field will be a little worse, but spectators won't lose much enjoyment, and may even gain enjoyment when poorly trained athletes do wacky things.
This is something I think about even more when in the cases of college or especially professional sports, where spectator enjoyment is a much bigger desideratum than it is in the high school case. Is my enjoyment dramatically enhanced by an increase in the quality of play? I've found the running game in college football more exciting than the running game in pro football, just because the lower quality of defense allows for more missed tackles and thus more exciting-looking runs. When we're weighing safety against quality of output in competitive sports, it makes sense to emphasize safety even more than it does in the more usual positive-sum activities.